The present invention pertains to broadband communications and more particularly to microwave monolithic integrated circuit (MMIC) amplifiers/baluns used in such communication systems.
Baluns are used in communication systems. Baluns may be used to convert RF signals from an unbalanced configuration, such as in a microstrip, to a balanced configuration. Such amplifiers/baluns may be used to drive mixer diodes, for example. MMIC 180.degree. hybrids are well suited for these implementations. However, broadband MMIC 180.degree. hybrids are difficult to realize because they are either too large in the physical sense to be realized in MMIC form or the output is too narrow in bandwidth to be useful.
Such baluns typically convert: 1) one input signal (unbalanced) to two output signals (balanced), 180.degree. out-of-phase; 2) two input signals, 180.degree. out-of-phase, to one output signal; and 3) two input signals to two output signals.
Simple distributed transmission lines implemented with vacuum tubes are well-known. However, such distributed transmission line circuits typically provide only one input and only one output.
Further distributed amplifier transmission line circuits have been developed. In such distributed amplifier transmission line circuits field effect transistors are employed. The gate and drain capacitances of these field effect transistors are used in conjunction with inductors to simulate transmission lines. Such circuits result in a transmission line which provides gain to the input signal. However, these circuits have only one input and one output.
Thus the circuits are not suitable for balanced signal applications.
It would be highly desirable to have a transmission line circuit for balanced-to-unbalanced conversion or unbalanced-to-balanced conversion in which a number of inputs and outputs may be handled and is suitable for implementation in MMIC-type design.